You are about to induce anesthesia on a 15-year-old girl for a thoracolumbar fusion when the surgeon casually mentions that, given the degree of kyphoscoliosis, a wake-up test might be required intraoperatively. Yikes! How does this affect your preoperative discussion with the child (and her parents) and your intraoperative management?

A wake-up test is one of several monitoring methods used to evaluate brain and spinal cord function during general anesthesia. The wake-up test allows an intraoperative neurologic examination, which is useful during surgery that may cause reversible central nervous system (CNS) injury. Wake-up tests are traditionally associated with scoliosis procedures during which significant spinal cord distraction may occur. Evoked potential monitoring is commonly performed during these procedures; however, the possibility of false-positive and false-negative results remains. A satisfactory motor response (achieved by asking the patient to “wiggle your toes” or “squeeze my fingers”) during a wake-up test reassures that both afferent and efferent spinal cord pathways are intact. Furthermore, a wake-up test is indicated in patients with persistent suppression of their evoked potentials despite correction of any identifiable cause and in cases of technical failure. Wake-up tests are rarely done during craniotomy when eloquent regions of brain are at risk (e.g., speech or motor regions). This subtopic is discussed more fully in Chapter 136.

The anesthesia provider must recognize that the potential complications of intraoperative wake-up testing are generally related to overzealous patient movement. These include injury to the patient, injury to operating room personnel, and dislodgement of monitors, intravenous lines, or airway equipment. Patient awareness of the wake-up test postoperatively is not necessarily an adverse event unless it is accompanied by awareness of discomfort. It is imperative that the anesthesiologist and patient discuss the wake-up test during the preoperative evaluation, both to acquire informed consent and to decrease potential for undesired patient movement. Patients should be reassured that the wake up will be brief, with maximum attention to their comfort level, and that recall of the wake-up test is possible but not likely.

In addition to discussing the plan with the patient, the anesthetic regimen should be chosen to facilitate a rapid and smooth emergence for the wake-up test. The earliest anesthetic techniques combined nitrous oxide, opioid, and a volatile anesthetic, allowing for rapid awakening. Since then, there has been some evolution in what is considered the optimum anesthetic technique for major neurosurgical procedures, driven by the use of more sophisticated intraoperative monitoring techniques. For example, motorevoked potentials (MEPs) are rapidly becoming the standard of care for major spine surgery. Unfortunately, transcranial MEPs are exquisitely sensitive to volatile anesthetics; thus, total intravenous anesthesia (TIVA), with some combination of propofol, ketamine, and opioid, is generally believed to provide the best MEP recordings under general anesthesia. Unfortunately, wake up from such an anesthetic may be prolonged. One recent trial compared two anesthetic techniques for wake-up testing and showed volatile anesthetic plus opioid (desflurane and remifentanil) allowed patient reawakening more rapidly than TIVA (propofol infusion with remifentanil or sufentanil).